It is very difficult to test the visual acuity (VA) of small children. It is nearly impossible to test VA in babies. It is definitely not possible to quantify it as we do with adults using the standard Snellen letter testing. The Snellen test is based upon recognizing specific letters of the alphabet. Visual acuity is calculated as the distance at which test is made divided by the distance at which the smallest optotype identified subtends an angle of 5 arcminutes. Small children cannot read the letters so there are Snellen charts made with pictures that subtend corresponding arcs. However these are of no use in children who have not learned to speak.
There remains a need for simple, inexpensive materials and methods for testing the visual acuity of infants, young children and others with limited communication skills.